This invention relates to temperature responsive measuring devices and more particularly to a universal connector and compensating terminal arrangement to be utilized in a temperature responsive instrument.
Presently, there are many instruments which are available which operate essentially as a temperature indicator or calibration instrument. As such, these instruments are capable of interfacing or receiving a thermocouple assembly or a resistance temperature device (RTD). Based on coupling to such devices, the instrument is capable of providing temperature calibration and/or temperature indication. The use of the thermocouple or RTD device with the instrument enables one to monitor temperatures in different environments. Such devices, as indicated, are available from many sources including the assignee herein.
Essentially, the instrument enables one to perform temperature measurements. These devices utilize curves which are indicative of thermocouples or RTDs to measure or simulate a temperature.
As such, the devices are referred to an temperature indicators/calibrators, and an example of such a device is the one sold by the assignee herein under the trademark MICROMITE II and available from Thermo Electric Instruments of Saddle Brook, N.J. 07662.
As indicated, these devices may be hand-held or may constitute a larger device. In any event, the devices have suitable plugs for accommodating various thermocouple devices as well as RTD devices. As one can ascertain, thermocouples and RTDs are available in many different configurations. As such, each different thermocouple or RTD device may have a completely different connector arrangement. The connector arrangements to thermocouple devices may also differ from those connectors which are utilized on RTD devices. Hence, such a unit preferably should employ a connector arrangement which can accept virtually any kind of input lead normally used on various types of thermocouples, as for example ordinary wire, standard and miniature thermocouple connectors, banana plugs, as well as three- or four-wire RTD's.
As is known, a thermocouple is a device which generates a voltage proportional to the difference in temperature between the hot and cold junction (reference junction). Such thermocouples generate such a voltage as a function of the metals or alloys incorporated therein. In any event, as indicated above, many different examples of thermocouples exist in the prior art. These thermocouples as indicated may be terminated in completely different connectors and can be utilized for example with a suitable temperature measuring instrument as the type described above if the instrument is capable of accommodating various connectors. As such, thermocouples which are available from many commercial sources including the assignee herein are terminated with mini plugs, regular size plugs, probes or essentially wire down to 12 gage.
Such an instrument should be capable of accommodating all the different types of thermocouple plugs in order to utilize the instrument efficiently. As is known, RTD configurations may come in three- or four-wire configurations and can also be terminated in a wide variety of plugs, and hence such devices must also be compatible with such an instrument. In the operation of thermocouples, the reference junction temperature of the thermocouple is normally monitored in order to obtain some reference temperature. This reference temperature can be room temperature or some other suitable temperature.
The problem involved with thermocouple measurement is that both the positive and the negative leads of the reference junction of the thermocouple must be maintained at equal temperatures, and that this temperature must be accurately measured by the thermocouple instrument. It is also important that the positive and negative terminals of the thermocouple instrument, which is also the thermocouple reference junction, be made of the same material and have similar impurities. This will remove any contact potential which may exist due to the coupling of the different thermocouples materials to the terminal assembly. The mass of the material of the terminal assembly needs to be large. This will create a large thermal inertia and will equalize the thermal response rate of the thermocouple reference junction and the reference junction temperature sensor which in this invention is a band-gap voltage reference imbedded in the negative terminal of the terminal assembly.
Once the potential difference is measured between the positive and negative wires of the reference junction of the thermocouple, and the temperature of the reference junction is accurately measured, the temperature of the hot junction can be calculated. This method of measurement is called reference junction compensation.
The prior art is cognizant of this problem and the problem has been explained for example in prior art references as well as various solutions to the same. See for example U.S. Pat. No. 4,488,824 entitled METHOD AND APPARATUS FOR PRECISION TEMPERATURE MEASUREMENT issued on Dec. 18, 1984 to R. J. Salem. This patent describes a band-gap voltage-reference and temperature sensor which is used to determine the temperature of the cold junction of a thermocouple for algebraic combination with the thermocouple signal to provide a precision temperature measurement at relatively fast speed. Thus, as can be ascertained from this particular reference, there is employed copper slugs which function as thermal inertia elements to equalize the thermal response rates of the temperature sensor and thermocouple.
The purpose of the device described is to equalize the thermal response at the cold junction and the band-gap device to temperature changes. The device utilizes a copper body which is stacked above another copper slug. The bodies are separated from each other by a thin layer of a quantity of a thermal conductive but electrically insulating material such as silicon grease.
Other patents such as U.S. Pat. No. 4,623,266 entitled COLD JUNCTION COMPENSATION FOR THERMOCOUPLE issued on Nov. 18, 1986 to J. A. Kielb. This patent describes a cold junction compensation bridge for a thermocouple circuit which includes a temperature compensation resistor encased in heat conducting material. This is directly connected to the same terminal block or strip to which the thermocouple leads are attached. In this particular patent the cold junction compensation resistor is in the same location as the junctions of the thermocouple to insure that any changes in temperature of the cold junction are sensed by the resistor.
As one can see from the above-noted references and others which exist in the prior art, there must be compensation of the cold junction and one must be sure that the temperature of both junctions are not affected by ambient temperature or not affected by any contact potential which may exist due to the coupling of the various thermocouple leads to the connector assembly. As indicated, these problems are known in the art as evidenced by the above-noted patents. Apart from this consideration which is a relatively major problem in regard to coupling or connecting thermocouples to various devices is the problem of accommodating a large variety and assortment of different connector techniques which may be associated with thermocouple devices.
It is therefore an object of the present invention to provide an improved connector and compensating block arrangement which is employed with a large number of various thermocouple devices to enable one to connect an instrument to such devices in an easy and reliable manner while further providing ambient temperature compensation for the reference junction as desired.